The present invention relates generally to the field of olefin polymerization catalysis, metallocene catalyst compositions, methods for the polymerization and copolymerization of olefins, and polyolefins. More specifically, this invention relates to olefin polymers having high Mz/Mw ratios, and the catalyst compositions and polymerization processes used to produce such olefin polymers.
In the polymer sciences, various measures of the average molecular weight of a polymer are utilized. For instance, Mn is the number-average molecular weight, Mw is the weight-average molecular weight, and Mz is the z-average molecular weight. The ratio of Mw/Mn is often used as a measure of the breadth of the molecular weight distribution of the polymer, and this ratio is also referred to as the polydispersity index. The ratio of Mz/Mw is a measure of the breadth of the high molecular weight fraction of the polymer molecular weight distribution.
Polyolefin homopolymers, copolymers, terpolymers, etc., can be produced using various combinations of catalyst systems and polymerization processes. One method that can be used to produce such polyolefins employs a metallocene-based catalyst system. Polyolefins having a unimodal molecular weight distribution, produced using a metallocene-based catalyst system, generally have relatively low Mw/Mn and Mz/Mw ratios. It would be beneficial to produce polyolefins using a metallocene-based catalyst system that have higher Mz/Mw ratios than conventional metallocene-based polyolefins. Accordingly, it is to this end that the present invention is directed.